The field of the present invention is generally that of a voltage regulating power supply circuit inputting electric power from a variable voltage DC source such as an automobile battery and outputting power at a fixed, stable voltage to a device such as a portable telephone, video camera, or CD player.
The SAE range of an automobile alternator is 16.2 to 10.8 volts. For best results, a car phone needs a fixed, stable DC source, at, say, 8 volts, ripple-free to minimize unwanted background noise.
To get the most possible use from a battery, the voltage regulating power supply must function as far down in the 16.2-10.8 volts range as possible. A disadvantage of a conventional power supply has been that it will not function with an input to output voltage drop of much less than 31/2 volts. This means it will not provide the required 8-volt output if the battery voltage drops below 111/2 volts. Further at a load of one ampere, heat dissipation in the order of 31/2 watts can become a serious problem in a compact assembly with miniaturized chip components.